Electrode assembly for gas tubes



Oct. 6, 1953 SMITH 2,654,850

ELECTRODE ASSEMBLY FOR GAS TUBES Filed Sept. 1, 1950 3 Sheets-Sheet l 5. 76% MM WW,

E- K. SMITH ELECTRODE ASSEMBLY FOR GAS TUBES Oct. 6, 1953 5 Sheets-Sheet 2 FIG.7.

Filed Sept. 1, 1950 U 5 U U Oct. 6, 1953 E. K. SMITH 2,654,850

ELECTRODE ASSEMBLY FOR GAS TUBES Filed Sept. 1, 1950 3 Sheets-Sheet 3 FlGn.10.

3n nentor W Gttorneg Patented Oct. 6, 1953 ELECTRODE ASSEMBLY FOR GAS TUBES Earle K. Smith, West Orange, N. J., assignor to Electrons, Incorporated, Newark, N. J.

Application September 1, 1950, Serial No. 182,678

24 Claims.

This invention relates to grid control gas tubes, and more particularly to the electrode assembly and mounting for such tubes.

It is desirable that grid control gas tubes for many applications and uses should be as small in their over-all dimensions and occupy as little space as practicably consistent with their rating, and should have a stable and consistent control of their firing by the prescribed grid potentials under the various operating conditions likely to be encountered in practice in the way of transient anode voltages or the like.

With these and other considerations in mind, the primary object of this invention is to provide a compact assembly of electrodes, together with the appropriate supporting elements and leads, which will reduce the over-all dimensions for a tube of a given rating, and still afford adequate stability of grid control for practical operating conditions.

Generally speaking and without attempting to define the nature and scope of the invention, it is proposed to support, insulate and electrostatically shield the electrodes of a grid control gas tube in a way to constitute a compact assembly of parts that may be enclosed in an envelope of small overall dimensions, and still have the desired stability of grid control and long life. More specifically, it is proposed to utilize insulating and metallic shielding elements in connection with the supports and leads for the electrodes of a grid control gas tube in a Way to provide a compact assembly, which may be mounted in a tube envelope of reduced length and diameter, with all of the electrode leads at one end of the envelope, and which will have the necessary conductive and electrostatic isolation of the electrodes and associated parts for stable grid control of the firing of the tube.

Various other characteristic features, attributes and advantages of the structural organization of this invention will be in part apparent, and in part pointed out as the description progresses.

Although the characteristic features of this invention may be embodied in various forms and types of tubes, it is convenient in describing the invention to refer to specific structures illustrated in the accompanying drawings as typical embodiments of the invention. In these drawings, Fig. 1 is a side view of the tube partly in section and having some parts broken away.

Figs. 2 to 5 are transverse sections through the tube taken on the line 2--2, 3-3, 4- 4 and 5-5 respectively indicated in Fig. 1 and looking in the direction of the arrows.

-' are supported,

2 Fig. 6 is a longitudinal section taken in part on the line 6- 6 indicated in Fig. 3, with the oathode shown diagrammatically, and illustrating more particularly the insulating elements for the grid lead and associated supports.

Fig. '7 is a fragmentary longitudinal section on the line '|--'l indicated in Fig. 4 and illustrating the anode supporting lead and associated shield and insulators.

Fig. 8 is a general view in perspective illustrating the skeleton framework forming part of the electrode assembly.

Fig. 9 is a general diagrammatical view illustrating the more significant features of the arrangement of the supports and shields for the electrodes.

Fig. 10 is a longitudinal section similar to Fig. 6 taken on the line lO-Hl in Fig. 12, and illustrating a modification of the grid mounting structure.

Fig. 11 is a transverse section through the tube taken on the line I Il I in Fig. 10 for this modification; and

Fig. 12 is another transverse section taken on the line [2-42 in Fig. 10, and illustrating the distposition of leads and supports for this modificaion.

The typical tube structure illustrated comprises in general an anode A, a control grid G, a coil filament or cathode C, a cylindrical metal shield S with transverse partitions and various connected elements for supporting, electrical insulating and electrostatically shielding these electrodes and associated parts in a tubular glass envelope E.

1 The electrode assembly is supported on a circular stem mount 5, which has its periphery fused to the tubular body of the envelope E, as indicated at 6, after the tube elements have been assembled on this circular stem mount 5 and are ready to be enclosed in the envelope E. The circular stem mount 5 has a circular row of bosses or beads adapted to anchor the ends of supporting rods, or provide a seal for through leads, as later described. The circular stem mount 5 is also provided with the usual central exhaust tubulation indicated at 7. In the particular structure illustrated, the various electrode leads are connected in the usual way to the pins in the porcelain part of a conventional base B, which has the upper edge of its metal shell attached to the tube envelope E by a suitable heat resistant cement, as indicated at 8.

- Considering first the form of the different electrodes, before describing the Way in which they insulated and electrostatically shielded, the anode A comprises a circular metal plate, preferably in the form of a thin sheet of tantalum, which has a down turned peripheral flange it and a circular rib H to stifien the tantalum sheet and avoid undue warping or distortion of such tantalum sheet as it is heated to a high temperature during fabrication and operation of the tube.

The grid G comprises a plurality of parallel bars l2 welded at their ends to end bars i3 (see Fig. 3). The grid bars l2 are preferably tungsten with a tungsten oxide coating in accordance with the disclosure of the prior patent of D. V. Edwards and E. K Smith, No. 2,021,339, August 27, 1935, so as to reduce the tendency for the grid to bemade unduly emissive by emissive material sputtered from the cathode. These grid bars are preferably spaced in accordance with the electrode spacing and other tube dimensions to provide the desired grid control ratio. It should be understood, however, that any suitable type oi a control grid'may be employed in the tube of this invention, and the grid bars l: for the type of gridiillustrated may be made if other metals, such as nickel, with the appropriate surface treatment or coating to reduce grid emission.

The cathode C in the tube structure illustrated comprises an oxide coated wire or filament shaped in the form of a coil or helix. This cathode C is preferably formed of a nickel core wire with an oxide coating of the barium nickelate type formed in the manner disclosed in the prior patent of D. V. Edwards and E. K. Smith, 'No. 2,081,864, May 25, 1937. The cathode C illustrated, however, is merely typical of one suitable for the type of tube shown, and various types of cathodes may be used in .the tube in this invention.

The shield S comprises a cylindrical shell l5 around a skeleton framework or cage (see Fig. 8) made up of a plurality of transverse partitions l6, H, 18 and I3, each having a peripheral flange, and connected by a plurality of longitudinal bars or straps 23 welded to such flanges. The two upper partitions l3 and I1 have central discharge openings 22 and 23 of the appropriate size; and these partitions l3 and IT, together with the cylindrical shell l5 of the shield S, form a compartment in which the grid G is located, as shown in Figs. 1 and 6. The two intermediate partitions i1 and I8, together with the cylindri cal shell 15, form a compartment enclosing the cathode C except for the discharge opening 23 in the partition H. The two lower transverse partitions l8 and [9 are solid except for small openings for insulators around the cathode and grid leads and a metallic shielding sleeve for the anode supporting leads later described. The shield S as a whole is supported by a plurality of legs, preferably three in number, in the form of rods 25 (see Fig. l), which have their lower ends anchored in bosses in the circular stern mount 5, and which have their upper bent ends welded to the underside of the bottom partition IQ of the shield S.

Considering now the way in which these various electrodes are mounted and supported, the ends of the cathode coil C are welded to the upper ends of a pair of cathode supporting leads 2! (see Figs. 1 and 5), which are sealed in the circular stem mount 5 at diametrically opposite points (see Fig. 4), and which extend through tubular insulators 28 of steatite or similar ceramic or like heat resistant insulating material. These insulators 28, which may have a snug fit in holes 29 in the two lower partitions I3 and I3, are preferably held in place by small protuberances on the cathode leads 2'! below these insulators, formed by deformation or pinching of the lead, or adding a smal1 spot of welded metal. The midpoint of the cathode coil C is electrically connected to the shield S by a wire or strap 30 welded to a center turn of this cathode coil and to the partition l8, as shown in the Figs. 1 and 4.

The supporting means for the grid G comprises a pair of rods 32 which are welded at their upper ends to the .end bars 13 of the grid, and which extend inside the shield S through tubular insulators 33 of steatite or the like to a point below the partition it of the shield S, where these rods 32 are welded to a cross connecting member 34 (see Figs. 5 and 6) shaped to clear the other parts of the assembly and provide a welded connection to the upper end of the grid lead 35, which is sealed in the circular stem mount 5 at the appropriate point. The lower portion of this grid lead 35 where it passes through the glass is formed of tungsten or other metal suitable for making the desired gas tight seal, and the upper part of this grid lead 35, preferably of nickel, together with the flexible basing wire, are butt welded to this tungsten piece, in the well known manner and in accordance with conventional practice, The same construction is employed for the other through cathode and anode leads; and the various dummy leads or supports anchored in the stem mount 5 are also preferably formed with tungsten ends to provide intimate metal to glass contact, and

, afford an anchorage of substantial stability and strength.

The tubular insulators 33 for the grid supporting rods 32 extend through openings in the intermediate partitions I! and I8 of the shield S, with such a fit in these openings as is conveniently obtained. Also, these grid support insulators 33 are formed with deep recessed, ends, as best illustrated in Fig. 6, in accordance with the disclosure of my prior Patent No. 2,456,540, December 14, 1948. Such recessed ends 38 for these insulators 33 serve to maintain, in the manner more fully described in said patent, the desired conductive isolation of the grid supporting rods 32 from the shield S, in spite of the tendency of these insulators to accumulate a surface film of sputtered or evaporated metal during fabrication or operation of the tube. As shown, these insulators 33 are assumed to be made in one piece with recessed ends, but may be formed of tubes of difierent diameter and length as disclosed in said patent. In order to hold these insulators 33 in place, each insulator is formed with a circumferential groove or recess, and a metal strap 39 seated in this groove is welded to an adjacent one of the longitudinal straps 20 of the skeleton framework of the shield S shown in Fig. 8.

The grid supporting lead 35 is electrically insulated from the lower partition IQ of the shield S through which it passes, and is also enclosed by a metal tube or sleeve 40 throughout its length between the shield S and the circular stem mount 5 of the tube envelope, as best shown in the Fig. 6. In the construction illustrated, a tubular insulator M, resting at its lower end on the projection or boss around the seal of the grid lead 35 in the stem mount 5, surrounds this grid lead inside of the metal tube All, and is formed with a recess at its upper end like the grid support insulators 33. This metal shielding tube 40 for the grid lead is secured to the lower partition l9 of the shield S. As illustrated, it is assumed that the upper end of this tube is slotted and formed with lips to be welded to the underside of this partition ill; but an auxiliary flanged eyelet or any other suitable arrangement of parts may be employed to obtain the desired mechanical connection.

The anode A in a tube 01? this invention, instead of having its supporting lead sealed in the upper end or the tube envelope E in accordance with common practice, has its supporting lead 44 sealed in the circular stem mount 5 at the same end of the envelope where the cathode grid supports and leads are located, and extends through the grid and cathode compartments inside the heat shield, as shown in Fig. 7. This anode supporting lead 44 is electrostatically shielded from the grid G and its connected parts and from the gas filling in the cathode region by a metallic shielding sleeve 45 connected to the shield S and at cathode potential, as well as electrically insulated from the other tube elements, for reasons later discussed.

In the construction shown and best illustrated in Fig. '7, a glass tube 46 around the anode lead 44 is fused to the boss around the seal for this lead in the circular stem mount 5, and the lower end of the shielding sleeve 45 fits over this glass tube 46. The shielding sleeve 45 extends through openings in the partitions Hi to IQ of the shield S with such clearance as convenient, and is attached to the shield S at its upper end by lips welded to the upper partition IS. A tubular insulator 48 of steatite of the appropriate length, and having a recessed upper end the same as the grid support insulators 33 previously described, surrounds the anode supporting lead 44 inside the shielding sleeve 45, and is held in place by crimping portions of said sleeve 45 into a circumferential recess in said insulator 48.

The anode supporting lead 44, thus insulated and shielded, extends to a point above the shield S where it is secured to the anode A. In attaching the anode A to the upper end of its supporting lead 44, the upper end of this lead is preferably welded to a suitable reinforcing element to obtain the desired stiffness and rigidity of support near the edge of a relatively thin sheet of tantalum. As shown, an arcuate bar 50 (see Fig. 2) preferably of iron or steel, is welded to the upper end of the anode supporting lead 44, and the tantalum anode is welded at a number of closely spaced points to this bar 50.

The anode A is preferably spaced closely to the top of the shield S, as shown in Fig. 1, in conformity with the disclosure of my prior Patent No. 2,489,938, November 29, 1949, for the purpose of decreasing ionic bombardment of the anode and minimizing the effects due to such bombardment.

A modification of the grid mounting structure above described is illustrated in Figs. 10 to 12. In this modification, two supporting rods 32a and 3219 are attached to the end bars 13 of the grid G; but these grid supporting rods, instead of being connected together by the cross member 34 and to a grid lead 35 as shown in Fig. 6, extend straight down to the circular stem mount 5, as best shown in Fig. 10, where one rod 32a is anchored in this stem mount, while the other rod 32b extends through a seal in the stem mount to constitute a through lead for the grid. These rods 32a and 321) are surrounded by tubular insulators 33a of steatite with recessed upper ends,

similar to the insulators $3 in Fig. 6. These tubular insulators 33a in the modification of Fig. 10 may be or a length to rest on the bosses or the stem mount 5; and since the upward. movement of these insulators is limited by the grid G, it is not necessary to provide auxiliary means, such as the band 59 shown in Fig. 6, for holding these insulators 33a in place. This simplifies the mounting procedure and avoids welding operations.

The lower end portions of each of the two grid supporting rods 32a and 32b, and their associated tubular insulators 33a, below the partition iii of the shield S, are surrounded in the modification of Fig. 10 by a metal shielding sleeve or tube 40a, similar to the tube 40 for the grid lead 35 in Fig. 6. The upper ends of these shielding tubes 40a are secured to the partition l8 of the shield S in a suitable manner, and their lower ends fit over the glass beads or bosses of the stem mount 5.

In this modification of the grid mounting struo ture shown in Fig. 10, both ends of the grid G are directly supported from the stem mount 5 by the rods 32a and 32b. In such an arrangement, the grid G may be readily mounted in the proper position, and will be maintained in such position with the desired rigidity, without being dependent upon the welded connections with the cross con necting bar 34 as in the structure of Fig. 6. Also, the lower partition IQ of the shield S required in the grid mounting structure of Fig. 6 to shield the cross connecting bar 34 and other exposed parts connected with the grid, may be omitted in the modification of Fig. 10, and the whole electrode assembly and tube may be made shorter.

Assuming the same mounting stem 5, with the same circular row of eight beads or bosses, the modification of Fig. 10 calls for a somewhat different disposition of leads and supports from the structure of Figs. 1 to 6. The supporting rods 32d and 32b for the grid G in the modification of Fig. 10 extend straight down to diametrically opposite bosses in the stem mount 5; and the resultant spacing between these rods makes the grid somewhat shorter, as can be readily seen by comparing Figs. 3 and 11. These diametrically opposite bosses in the stem mount 5 for these grid supporting rods 32a and 32b are preferably adjacent the bosses for the cathode leads 21, and the boss for the anode supporting lead 44 is spaced from the bosses tor these grid supporting rods, as shown in Fig. 12. The three supporting legs 25 for the shield So in the modification of Fig. 10 are anchored in the remaining bosses of the stem mount 5, as shown in Fig. 12; and although these legs 25 are not equally spaced, the metal shielding tubes 40a. around the grid supporting rods help to support this shield.

The tube structure just described may be as sembled and mounted by ordinary welding operations in the appropriate sequence. Starting with the shield supports 25 and the electrode leads 2!, 35 and 44 secured in the circular stem mount 5, the assembly may be built up by adding the vari ous parts and making the necessary welding connections in the appropriate order. This mounting procedure is greatly facilitated by the skeleton framework for the shield S (see Fig. 8) which enables the several transverse partitions I5 to IQ of this shield to be applied in turn and secured in the proper space relation by welding them to the straps 20, as the assembly of parts and welding operations progress, the space between these partitions and their connecting straps 20 affording the desired accessibility to the parts to be welded together. The cylindrical shell 15 of the shield S may be slipped in'place and welded to flanges of the upper and lower partitions It and 19 as a final step in the mounting procedure. In fact, a shield structure of this type, made up or" a skeleton framework and a separate cylindrical shell, makes it possible to make the welding connections inside of the shield for the compact electrode assembly characteristic of the invention.

After the assembly of electrodes and shield on the circular stem mount is completed and inserted in the body of the envelope E, and the periphery of this mount 5 is fused to the wall of the envelope, the tube is subjected to the appropriate schedule for de-gasing and exhaust, including the formation and activation of the oathode oxide coating; and the envelope is filled with a suitable ionizable gas, such as Xenon, at the appropriate pressure, whereupon the exhaust tubulation I may be sealed off and the base B attached in the usual way.

One significant feature of the tube of this in vention is that the anode A is supported by its lead 44 from the same end of the tube envelope as the cathode and grid, rather than at the other end of the envelope in accordance with common practice. This materially decreases the space requirements for the tube, since the envelope is shortened by the distance that would otherwise be required for an adequate seal for the anode lead and a suitable terminal cap. Also, the supporting, insulating and shielding elements for the anode and grid are disposed inside the shield S; and the diameter of the tube need not be much larger than the diameter of the shield S, which in general must have certain appropriate dimensions for a tube of a given rating and operating characteristics regardless of the of the tube envelope. Thus, the organization or parts char acteristic of this invention for supporting and mounting the electrodes, together with the associated insulating and shielding elements, gives a desirable reduction in the over-all dimensions of the tube for its capacity or rating, as compared with other arrangements for mounting and supporting the electrodes in a hot cathode grid control gas tube.

For many complications and uses of a grid control gas tube, it is important to have uniform and. consistent control of the firing of the tube in respons to prescribed voltages to its grid. Among other things, it is d "able that abrupt changes in the potential of the anode, due to voltage spikes or transients in the anode voltage sometimes encountered in practice, should not materially ailect the control of the firing of the tube by its control grid. In th tube of this invention, where the control grid is located in a compartment between the transverse partitions it and ll of the shield S at cathode potential, the anode to grid capacity is relatively low and substantially uniform, the upper partition acting to shield a large part of the grid surface from the anode A. Also. the metal shielding sleeve at cathode potential around the anode supporting lead M serves to electrcstatically shield this lead from the grid G and its supports or connected parts, and from the region of the gas filling around the cathode C. In other words, even though the anode supporting lead extends inside oi the shield S in the interests of space reduction, it is adequately shielded electrostatically by th shielding sleeve 55 from the grid and its associated parts and the region adjacent the cathode, so that the efiective control of the grid is not materially affected by transient anode voltages.

Considering the mounting of the control grid G in the tube of this invention, it will be noted that this grid is supported at both ends, and hence may be readily assembled in th proper space relation to the other parts, and may not be materially shifted by jar or vibration. The insulators 33 around the grid supporting rods 32 insulate these rods from the partitions H and E8 of the shield S, and also electrically isolate these rods from any active material sputtered from the oathode C that might otherwise accumulate and tend to cause electron emission and interfere with the desired grid control.

In general, the actual potential of the grid G relative to the cathode C at a given instant determines whether or not the tube will fire; and for consistent grid control by a prescribed voltage impressed on the grid, it is desirable to avoid the application of extraneous potentials to the grid or parts connected with it. It is found that, in addition to the shielding for the anode supporting lead as previously explained, consistent and dependable grid control calls for isolating the grid supporting rods and grid lead inside of the tube envelope from the gas filling and the tube walls. Complex phenomena ar involved in the ionization and deionization of the gas filling of a tube when in operation; and if parts connected with the control grid G, such as the supporting rods 39., have substantial surfaces exposed to the gas filling, there may be 'sufiicient electronic or ionic grid current to interfere with th desired grid control. characteristics of the tube. Also, during operation of the tube there app-ears to be a tendency for the inner walls of the tube envelope to accumulate charges and establish potentials that under some conditions adversely affect the desired grid controlling action.

Accordingly, in the tube of this invention, provision is made for conductively and electrostatically isolating the grid supporting and leadin elements, so as to obtain a more consistent grid control of the firing of the tube under conditions sometimes encountered in practice. The tubular insulators 33 conductively isolate the rods 32 connected with the grid G from the gas filling in the cathode region, thereby preventing these parts connected with the grid from receiving electrons or ions before or during ionization and conduction through the tube, and eliminating electronic or ionic current that might otherwise interfere with the desired controlling action of the grid. In the tube structure of 1, the shield S, together with its lower partition l9, electrostatically shields from the walls of the tube envelope the lower ends of the grid supporting rods 32 outside of the cathode compartment, the cross connecting member as, and the upper end of the grid lead 35. Similarly, the metal shielding sleeve 49, connected to the shield S, surrounds the grid lead 35 throughout its length between the shield S and the lower end of the tube envelope formed by the stem mount thereby electrostatically shielding this grid lead 35 from the walls of the tube envelope. Thus, the surfaces of these parts connected to the grid are electrostatically shielded by metal surfaces at cathode potential from charges that may accumulate on the inner walls of the tube envelope, and might otherwise induce extraneous grid potentials to interfere with the desired grid controlling characteristics of the tube.

In the modification of the grid mounting structure shown in Figs. 10 to 12, the cross connecting member 34 and its exposed welded connections with the rods 32 and lead 35, characteristic 9 of the grid mounting structure of Fig. 1, are not used; and the lower partition IQ for the shield S may be omitted; but the portions of the grid. supporting rods 32a and 32b in this modified structure outside of the shield are surrounded by shielding sleeves or tubes a extending down to the lower end of the envelope formed by the stem mount 5.

In connection with the significance of the shielding means disclosed, it has been observed that the inner walls of a gas tube envelope tend to accumulate during fabrication and use a layer or fihn of sputtered or evaporated material from the metal parts; and to the extent that such film may be continuous and conductive, it is likely that the metal shielding sleeve connected to the shield S and to the cathode and contacting with the glass envelope, serves to drain oii charges on the tube walls and prevent the clevelopment of high potentials that might affect the potential distribution in the grid to anode region and modify the controlling influence of the prescribed grid voltages applied tto the grid. The action of the shielding sleeve 40 in this respect depends upon factors of a variable character and diflicult to evaluate; but it is characteristic of the shielding arrangement for the grid lead 35, as well as the anode lead 44, in the structure illustrated and preferably employed,

that some drainage and dissipation of tube wall charges may exist, and this may contribute to the stability of grid control obtained by this invention.

The specific structures shown and described for supporting, insulating and shielding the electrodes in a grid control gas tube provide the small over-al1 dimensions and consistent grid control characteristics for a grid control gas tube desirable for many applications and uses of such tubes. These specific embodiments of the invention disclosed, however, are merely typical, and various adaptations, modifications and additions may be made in the particular construction and arrangement of parts shown and described without departing from the invention.

What I claim is:

1. In a grid control gas tube, a gas filled envelope containing a compact assembly of electrodes and supporting elements closely spaced to the walls of said envelope, said assembly comprising a cylindrical shield having separate compartments around a hot cathode and a control grid, an anode closely spaced to the grid compartment, supporting means for said electrodes including leads sealed in one end of the envelope and parts inside said shield, said means including metallic shieldin surfaces at cathode potential electrostatically isolating the parts of the anode supporting means from the parts of said grid supporting means both inside and outside of said shield.

2. In a grid control gas tube, an electrode assembly of a shielded hot cathode, control grid and anode comprising, a cylindrical shield having a skeleton framework of transverse spaced partitions and longitudinal connectin straps surrounded by a cylindrical can, said shield forming separate compartments enclosing said cathode and said control grid except for openings for the passage of a discharge between the cathode and anode under the control of said grid, and means supporting said electrodes in a predetermined space relation to said shield and including welded parts inside said shield, said skeleton framework facilitating the assembly. and inter- 10 connection of the parts of said supporting means located inside of the shield.

3. A grid control gas tube comp-rising, a gas filled envelope containing a .hot cathode, control grid, and anode, a metallic shield connected to said cathode and forming separate compartments enclosing said cathode and said control grid respectively except for openings for the passage of a discharge current between said oath ode and anode under the control of said control grid, supporting leads for said grid extending through the cathode compartment, and insulating means of heat resistant material electrically isolating said grid supporting leads from said shield and also from thegas filling in the cathode compartment.

4. A grid control gas tube comprising, an envelope containing an ionizable gas and a plurality of electrodes including a hot cathode, a control grid and an anode, a cylindrical metallic shield at cathode potential having a compartment wholly enclosing the emissive surface of said cathode except for a discharge opening for the passage of electron current to the anode under the control of said control grid, said shield including a member having a discharge opening therein and interposed between said control grid and said anode, means rigidly supporting all of said electrodes and said shield from one end of said envelope in a predetermined space relationship, said means including a pair of grid supporting rods extending from said end of the envelope to the grid at substantially diametrically opposite points of the axis of the tube, one of said grid supporting rods being sealed in said end of the envelope to constitute a grid lead, said grid supporting rods extending for part of their length inside of said shield, and tubular insulators of heat resistant material around said grid supporting rods to engage said shield at spaced points and to surround the surfaces of said rods exposed to the gas filling in said shield, whereby the control grid is maintained in position by said shield in cooperation with said grid supporting lead, and parts at grid potential are electrically isolated from said shield and the gas filling therein.

5. A grid control gas tube comprising, a gas filled envelope containing an oxide coated cathode, control grid and anode, a cylindrical shield around said cathode and connected thereto, said cathode shield having two spaced partitions at one end with central discharge openings therein, said anode being closely spaced to said. end of said shieldopposite said discharge opening, said control grid being located between said. spaced partitions of said cathode shield, and means supporting said electrodes in a predetermined spaced relation to said shield and including tubular insulators of heat resistant material and separate insulated. electrode leads sealed in the same end of the envelope.

6. In a grid control gas tube comprising, an envelope containing a gas filling, an oxide coated hot cathode, control grid and anode, a cylindrical shield having spaced transverse partitions enclosing said cathode and control grid in separate compartments except for discharge openings in said shield for the passage of an arc discharge between the cathode and anode through the control grid, and a plurality of supporting leads for said control grid extending through the region around said cathode inside said shield, and tubes of steatite having recessed ends and disposed around said grid supporting leads to insulate them from the partitions of said shield and from the gas filling in the cathode compartment.

7. A grid control gas tube comprising, a gas filled envelope containing an oxide coated hot cathode, a control grid and anode, a cylindrical metallic shield at cathode potential forming separate compartments enclosing said cathode and said control grid respectively except for openings for the passage of a discharge between the cathode and anode under the control of said control grid, supporting leads for said grid extending through the cathode compartment, tubular insulators of heat resistant material around said grid leads where they pass through the partitions of the cathode shield and where they are exposed to the gas filling adjacent the cathode, and supporting means for said anode including a supporting rod encircled by a metallic sleeve but electrically insulated therefrom, said sleeve being attached to said cathode shield and shielding said anode rod throughout the portion of its length adjacent its control grid and supporting means.

8. A grid control gas tube comprising, a gas filled envelope containing an oxide coated hot cathode, a control grid and anode, a cylindrical shield having transverse partitions forming separate compartments enclosing said cathode and grid except for openings for the passage of a discharge between the cathode and anode under the control of the control grid, means supporting said electrodes from the same end of the envelope and including separate supporting leads for said grid and anode extending adjacent each other through partitions in said cathode shield, a tubular insulator around the grid supporting lead where it passes through the partitions of said 7 cathode shield and through the cathode compartment, a metallic sleeve around said anode supporting lead to isolate it electrostatically from said grid and its supporting means, and a tubular insulator in said sleeve around said anode supporting lead, said tubular insulators being of a heat resistant material and having recesses in their exposed ends.

9. A grid control gas tube comprising, an envelope filled with an ionizable gas and containing a hot cathode, control grid and anode, a cylindrical heat shield at cathode potential in said envelope and having a compartment wholly enclosing the emissive surface or" said cathode except for a discharge opening for the passage of an arelike discharge current to the anode under the control of said control grid, and means including a plurality of separate supporting leads sealed in the same end of said envelope for rigidly supporting all of said electrodes and said shield in a predetermined space relation and for providing independent external electrical connections to said cathode, control grid and anode, the space relationship of said anode and grid supporting leads thus sealed in the same end of the envelope resulting in considerable capacitance between them, said shield having metallic surfaces at cathode potential shielding said anode supporting lead throughout its length from said control grid and the parts of its sup-porting means at grid potential, whereby said control grid and connected parts at grid potential are electrostatically shielded. from abrupt changes in anode tallic shield at cathode potential having a com partment wholly surrounding the emissive sur face of said cathode except for a discharge opening, an anode opposite said discharge opening, a control grid governing the passage of a discharge current through said discharge opening from said cathode to said anode, supporting leads for said electrodes all sealed in the same end of said envelope, the supporting lead for said anode extending inside of said shield adjacent said grid supporting lead, a metallic sleeve connected to said shield and disposed around said anode supporting lead substantially throughout its length, and insulating means of heat resistance material between said sleeve and said anode supporting lead in engagement therewith at a plurality of points along its length, whereby said anode supporting lead is electrostatically shielded by said sleeve at cathode potential from surfaces at grid potential, and is maintained in position out of contact with said metallic sleeve by said insulating means.

11. A grid control gas tube comprising, a sealed envelope containing an ionizable gas filling and electrodes including an anode, a control grid, and a hot cathode, a shield around said cathode limiting ionization of the gas filling by anode potentials to a path through said control grid, said shield being electrically connected to a point on said cathode, separate insulated supporting leads for said electrodes sealed in one end of said envelope, the supporting lead for the anode extending through a region adjacent the control grid and its leads inside said cathode shield, and means conductively and electrostatically isolating said anode supporting lead, said means including a metallic sleeve attached to said shield and a bushing of heat resistant insulating material around said anode lead inside said metallic sleeve, said bushing having a recessedend, to prevent the deposit of vaporized metal on its end forming a conductive path between said anode lead and said metallic sleeve.

12. A grid control gas tube comprising, a gas filled envelope containing electrodes including a hot cathode, control grid and anode, a shield having a compartment surrounding said cathode except for an opening in one end for discharge between said cathode and anode, said grid being located in the path of such discharge, means supporting said anode and said control grid from the same end of the envelope and including separate supporting leads for said anode and said 'grid extending adjacent each other through the including an oxide coated hot cathode, controls grid and anode, a metallic shield having a compartment surrounding said cathode except for an opening in one end for the passage or a discharge between the cathode and anode under the control of said control grid, means supporting said electrodes and said shield in said envelope and including separate leads for said electrodes.

sealed in'one end of the envelope, said anode hav-- ing a supporting lead extending inside of said shield through a region adjacent said control grid and its leads, means including a metallic sleeve for isolating said anode lead electrostatically throughout said region from said control grid and its leads, said grid supporting means including a rod passing through the ends of said cathode shield, and a tubular insulator of heat resistant material around said grid supporting rod insulating it from the ends of said cathode shield and from the gas filling adjacent said cathode.

14. A grid control gas tube comprising, an envelope having a stem mount at one end and containing a hot cathode, control grid and anode in an ionizable gas filling, a metallic shield at cathode potential nearly as large in cross section as said envelope and including a compartment. wholly enclosing said cathode except for a discharge opening, said control grid and said anode being located in closely spaced relation opposite said discharge opening, said shield including a member with a discharge opening therein interposed between said anode and said grid, means including supporting leads sealed in the stem mount of said envelope for supporting all of said tube elements from one end of the envelope, said supporting leads being separately connected with said cathode, control grid and anode and being disposed in part inside of said shield, and insulators of heat resistant material electrically insulating said leads from said shield, and metallic parts connected with said shield and having surfaces at cathode potential between the parts connected with said anode and the parts connected with said grid both inside and outside of said shield, whereby said control grid is electrostatically shielded from the efiect of abrupt changes in the anode supply voltage.

15. A grid control gas tube comprising a gas filled envelope containing an oxide coated hot cathode, a control grid and anode, a metallic shield surrounding said cathode except for an opening for the passage of a discharge between said cathode and anode under the control of said control grid, means supporting said control grid including a lead extending through the gas region inside of said. cathode shield, and a tubular insulator of .heat resistant material around said grid lead extending through the ends of said cathode shield, said tubular insulator having a deep contracted recess in the end exposed to metal vaporized during fabrication or operation of the tube and likely to form a conductive film on such exposed end. i

16. A grid control gas tube comprising an oxide coated hot cathode, a cylindrical shield surrounding said cathode except for a discharge opening at one end, a control grid adjacent said discharge opening, a pair of grid supporting leads extending through the ends of said cathode shield and through a region inside said shield adjacent the cathode, and a tubular insulator of heat resistant material havin recessed ends and surrounding each grid lead where it passes through the ends of said cathode shield and through said region adjacent said cathode.

17. A grid control gas tube compnsing, a gas filled envelope containing a hot cathode, control grid and anode, a cylindrical shield at cathode potential having a compartment wholly enclosing the emissive surface of said cathode except for an opening for the passage of a discharge current between the cathode and the anode under the control of said grid, means including a plurality of metallic supporting leads and tubular 14 insulators of heat resistant material for supporting said electrodes and said shield from the same end of said envelope, said means including a plurality of supporting leads for said grid extending for a portion of their length inside of said shield, tubular insulators for conductively insulating said portions of said grid supporting leads from the gas filling in said shield, and a metallic sleeve at cathode potential around said grid supporting lead throughout the portion of its length between said shield and the wall of said envelope.

18. A grid control gas tube comprising an evacuated envelope containing a hot cathode, control grid and anode in an ionizable gas filling, a cylindrical metallic shield at cathode potential having a compartment wholly enclosing the emissive surface of said cathode except for a discharge opening for the passage of electron current from the cathode to the anode under the control of the control grid, means supporting all said electrodes and said shield from the same end of said envelope, said means including separate grid and anode supporting leads sealed in said end of the envelope and extending straight from their seals in a general parallel relation through said metallic shield, said shield having surfaces at cathode potential electrostatically shielding said anode supporting lead substantially throughout its length from said control grid and its supporting lea-d, and a metallic sleeve connected to said shield and surrounding said grid supporting lead throughout the portion of its length between its seal in said end of the envelope and said shield. l

19. In a grid control gas tube, a gas filled envelope containing a hot. cathode, control grid and anode, a cylindrical shield having transverse partitions forming a compartment enclosing said cathode except for an opening for the passage of a discharge between the cathode and anode under the control of said grid, and means supporting said electrodes and shield from one end of the envelope and electrostatically shielding parts at anode and grid potentials from each other and the walls of the, tube envelope, said supporting means including leads and welded connections located in part inside of said shield, said shield comprising a cylindrical can around a skeleton framework of longitudinal straps supporting said partitions to permit the assembly and Welding of the parts of said supporting means inside of said shield.

20. A compact assembly of electrodes and shielding means for grid control gas tubes comprising, a sheet metal shield consisting of longitudinal straps supporting spaced transverse partitions and a cylindrical can around said straps and partitions, a hot cathode, a control grid, and means including welded connections inside said shield for supporting said cathode and control grid in separate compartments between transverse partitions of said shield.

21. A grid control gas tube comprising, a gas filled envelope having a circular stern mount at one end and containing a hot cathode, control grid and anode, a pair of leads for said cathode sealed in said stem mount, a pair of supporting rods for said grid anchored at one end in said stem mount, one of said rods being sealed in said stem mount to constitute a through grid lead, a supporting lead for said anode sealed in said stem mount, a cylindrical metallic shield at cathode potential supported by said stem mount and including a compartment wholly enclosing said cathode except for a discharge opening opposite '15 said grid and said anode, said shield having its outer wall closely spaced to the inner wall of said envelope and surrounding portions of said grid supporting rods and said anode supporting lead, and positioning elements of heat resistant insulating material having a fixed relation to said shield and engaging said grid supporting rods and said anode supporting lead respectively each at a plurality of separated points along its length, said shield having metallic surfaces at cathode potential disposed between opposing surfaces of said grid supporting rods and said anode supporting lead, whereby said electrodes are all supported from one end of the envelope and are maintained by said insulated positioning elements and said shield in the desired space relationship, and said control grid is conductively insulated and electrostatically shielded to afford consistent grid control.

22. A grid control gas tube comprising, a gas filled envelope containing a hot cathode, control grid and anode, a metal heat shield enclosing said cathode except for a discharge opening, a control grid between the discharge opening in said cathode heat shield and said anode for controlling the firing of the tube, a pair of grid supporting leads extending from the grid inside of said shield to seals in a Wall of said envelope, said grid leads being insulated from said heat shield and from the gas region around said cathode by tubular insulators of heat resistant material, and a metallic sleeve around each of said grid leads connected to and extending from said shield to the wall of said envelope.

23. A controllable gaseous discharge tube comprising an' evacuated envelope having a circular stem mount at one end and containing an ionizable gas filling, an oxide coated cathode maintained at an emissive temperature by heating current from an external source, an anode having an extensive surface for receiving a discharge current from said cathode, a control grid between said cathode and said anode acting to through said heat shield and supporting all of said electrodes from said circular stem mount, said supporting elements including a pair of leads for supplyingcurrent for heating said cathode and separate leadsfor said control grid and said anode, tubular insulators of heat resistant material insulating all of said leads from said heat shield, and means comprising metallic surfaces connected with said heat shield for electrostatically shielding the adjacent portions of said grid and anode leads both inside and outside of said heat shield, whereby said control grid and connected parts are electrostatically shielded from abrupt changes in anode potential due to tran sients in the anode supplying voltage.

24. A grid control gas tube comprising, an evacuated envelope containing an ionizable gas and enclosing an electrode assembly of a heat shielded hot cathode, control grid and anode, said cathode having an oxide coated emissive surface maintained at the emissive temperature by heating current supplied from an external source, said control grid being disposed between said cathode and said anode to control initiation of a discharge current between said cathode and said anode, a heat shield comprising a skeleton framework connected with transverse partitions and a cylindrical shell to form compartments enclosing said cathode and said control grid separately except for discharge openings for the passage of discharge current between said cathode and anode under the control of said control grid, means including rods extending inside and in part through said heat shield for supporting all of said electrodes from the same end of the tube envelope and affording separate lead-in con nections to the respective electrodes, tubular insulators of steatite insulating said rods from said heat shield, and metallic sleeves connected with said heat shield and acting to electrostatically shield all parts at grid potential from the supporting elements of said anode both inside and outside said heat shield and from the walls of the tube envelope outside said heat shield, whereby the controlling potential applied to said control grid is not adversely'afiected by abrupt changes in anode potential or by charges accumulated on the envelope walls.

EARLE K. SMITH.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,044,618 Livingston -2 June 16, 1936 2,203,639 Smith June 4, 1940 2,297,721 Smith Oct. 6, 1942- 2,356,566 Clark et a1 Aug. 22, 194 2,456,540 Smith Dec. 14, 1948 2,462,142 Stutsman Feb. 22, 1949 

